Need help with an error check

I'm trying to do an error check on a JTextField where the correctinput can be -999 to 1000. I've figured out how to check for "" &length >4, but I'm completely lost as to how to do the "-" and checkto make sure the answer is numeric and not alpha. I'm supposed to beusing "String" methods for my error checks. Here's what I've gottenso far:

public void actionPerformed (ActionEvent ae){int inputTemp=0;//initialization of the sourceTemp to zero